Gas discharge excess voltage arrester

ABSTRACT

A compact highly efficient multipath gas discharge type excess voltage arrester comprises first and second axially aligned electrodes projecting in opposite directions through a metallic end cap means to a point within a tubular third electrode. The metallic end caps are each constructed of a pair of axially aligned oppositely disposed first and second dished members which each have a facing groove receiving an insulating ring member in sealing relation. The walls of the frusto conical dished members serve to protect the insulating ring from metallic electrode vapors. The metallic end cap means close opposite ends of a tubular third electrode means to form the gas discharge tube. Contact members of the first, second and third electrodes extend beyond the ends and circumference respectively, to provide additional protection for the end caps and insure structural integrity of the arrester.

United States Patent 1191 l2/l966 Gray 317/61 Lange 5] Nov. 27, 1973 GASDISCHARGE EXCESS VOLTAGE ARRESTER Primary Examiner-J. D. Miller [75]Inventor: Gerhard Lange, Berlin, Germany jifgfgfigigz fif g Fendelman[73] Assignee: Siemens Aktiengesellschaft, Berlin &-

' Munich, G y 1 57 ABSTRACT [22] Filed: Nov. 30, 1971 A compact highlyefficient multipath gas discharge t e excess volta e arrester com risesfirst and second [2]] App! 203377 azt ially aligned el ctrodesprojeciing in opposite direcv tions through a metallic end cap means toa point [30] Foreign Application P io it D t wthin a tubular thirdelectrode. The metallic end caps Jan.- 25, 1971 Germany o 71 02 611.4are each. constructed a Pair axially aligned sitely disposed first andsecond dished members which 52 us. (:1. 317/615, 317/62 each have facingreceiving an insulating ring 511 rm. c1. H02h 3/22 memberin Sealingrelation The walls of the frusto [58] Field of Search, 3 17/61 61.5 66,mica! dished members Serve to prom:t h insulating 7 337/28, 31 32315/36; 313/220, ring from metallic electrode vapors. The metallic end282,312, DIG. 5 cap means close opposite ends of a tubular thirdelectrode means to form the gas discharge tube. Contact 5 ReferencesCited 1 members of the first, second and third electrodes ex- UNITEDSTATES PATENTS tend beyond the ends and circumference respectively, toprovide additional protection for the end caps and 53:2: 't 3 3 insurestructural integrity of the arrester. 3,292,030 6 Claims, 1 DrawingFigure This invention gen erally'relates toja gas discharge type excessvoltage arrester having a pair of electrodes The first dished member ofthe metallic end cap'has an opening just large enough to allow thecylindrical electrode to 'pass'therethrough'anda contact member providesa's'eal on the outside of the opening. In this which are arrangedopposite eachother so that their innerends'are spaced from each other ina gas tight dischargechamb'erofa multipath discharge tube. A'cylinydricall y shaped third electrode separates alpair of metallic endscaps which close the ends of the third electrode in gas tight relation.The first and second electrodes are cylindrical rods which are arrangedcoaxially and extend through the metallic end caps into the dischargechamber.

Multipath excess voltage arresters are well known in the art as shown,for example, by the German Letters Pat No. 930,400 and 1.089.482. Theyhave the advantage in that a first discharge on one path pre-ionizes thegas in the discharge chamber of the excess voltage arrester so that the"ignition of the seconddischarge path .is accelerated. There are a numberof essential requirements for these multipath arresters. Thus, theremust be sufficient insulation of the electrodes from each other evenafter the arrester has been loaded or stressed. In addition, they mustprovide for the formation of a permanent short circuit when theelectrodes are overloaded and there must be a high reliability of thevacuurn density of the discharge tube and a low reaction ir'n'pactvoltage. In addition to the foregoing requirements it is important thatthearrester be as compaet'in construction as possible. While theserequire- SUMMARY OF THE INVENTION arrester wherein first" and secondmetallic end caps closing opposite ends of a tubular cylindricalelectrode form the discharge tube with the metallic end caps each mentshave been known to those skilled in theart there has neverthelessb eenalong standing. need for an excess voltage arrester which meets allofthe above noted requirements.

being constructed of first and second dished members which dishedmembers have a first end and a second end with thesecondendhavingflaterally projecting grooved rim thereabout so that thefirst ends face towards each other and the secondends face away fromeach other with the tubular insulating ring having oppositeend edgesreceived in the-grooves of the rims.

' The insulating ring is of a length whereby the firstends of the dishedmember are spaced I from each other. Each of the first andsecondmetallic end capshas a respective first and second electrodeextendingthrough openings in thefirst end of eachof the dishedmemberswhereby the inner ends of the first and second elec- I ing ringfromthe discharge-chambers of the discharge tube. The metallic end capsmay take'theform of a frustum of a cone and be of a metallic'materialwhich has a thickness less then that of the adjacent electrodes.

way the first dished member is in electrical contact with its respectiveelectrode. At the same time the second 1 dished member of the metallicend cap is spaced from the first dished member and is in electricalcontact with exceeds the largest lateral dimension of the voltagearrester. The contact members of the first and second electrodesprojectbeyond the ends of the metallic cap members. In this way thevoltage arrester forms a very compact construction. The discharge tubecontains a gas which gas may be preionized by substance receivedin thetube. v j

The voltage arrester according to the invention meets the requirementsset forth above and overcomes the deficiencies of the prior art by meansof its combination of features. Thus, the shading ofthe portions of'th'einnersurface of the insulator rings will assure that the electrodematerial does not evaporate due to the arc discharge which occurs in thechamber. Aslo, it prevents conductive bridges from forming on insulatorrings and thus maintains the integrity of the insulation between theelectrodes. The frustum shape of the surface also gives a certainelasticity to theidished members which connect the electrodes with theinsulator rings'to thereby increase the safety with respect to thefracture of the discharge tube. Since the wall thickness I of thefrustum shaped surface is designedlto be less then that of the adjacentelectrodes a heat conductivity towards the insulator rings is lowered sothat they are protected from over heating which over heatin'g'rnightburst the insulator rings. The insulating rings are advantageously madeof a ceremic material and sealed in the grooves with a glass sealant.This seal connection is protected from harmful thermic influences due tothe provision of massive contact members for the electrodes whichcontacts have a dimension that surpasses the dimension of the otherportions of the excess voltage arrester. This design assures that thecurrents which flow through the arrester travel only via the mentionedmassive contact members and are not further guided through the metalpartsof the discharge tube that are connected to the insulator rings.

The excess voltage arrester according to the invention has the furtheradvantageous property of being able to short circuit when overloadedwhich short circuit is caused by the melting off of the top of therodlike electrodes during an overload to thereby produce a conductivebridge which extends towards the hollow cylindrical electrode.Because'of the coaxial arrangement of the hollow cylindrically shapedcentral or third electrode about the ends of the first and second rod-'like electrodes a very dynamic arrester is produced which has a lowerreaction impact voltage. In orderto lower the reaction impact voltagestill further the dis charge chamber of the discharge tube maybe'provided with at least a piece of a material which preionizes the gasin the tube.

BRIEF DESCRIPTION OF THE DRAWING M Other objects, featuresand advantagesof the invention will be readily apparent from the following descriptionof a preferred embodiment thereof,,taken in conjunction with theaccompanying drawing, although variations and modifications may beeffected without departing from the spirit and scope of the novelconcepts of the disclosureand in which:

The FIGURE is a longitudinal cross section view of a gas dischargemultipath excess voltage arrester according to the invention.

Referring to the drawing it may-be seen that the two 'path excessvoltage arrester according to the invention generally indicated atincludes a first electrode 1 extending through an end cap meansgenerally indicated at l l and a secondelectrode 2 extending through asecond end cap means generally indicated at 12. A third generallytubular electrode 3 has its first end 30 closed by the first end capmeans 11 and its second end 3b closed by the second end cap means 12 toform a gas tight multipath discharge tube. v

The first and second electrodes 1 and 2 respectively take the form ofcylindrically shaped rods which are coaxially arranged with their firstends 1a and 2a respectively, spaced from each other and located in a 7central portion of the discharge tube surrounded by the third electrode3.

end 4a has an opening 4d therein of a size to just receive the firstelectrode 1 therethrough so that only the thin end wall at end 4a is incontact with an adjacent portion of electrode 1. A massive contact 8extends beyond the hole and forms a seal about the electrode 1. A seconddished member 6 has a first end 6a and a second end 611 which second endis configured similar to the second end 4b to have a groove 60 therein.The first end 6a has an opening 6d therein of a diameter larger then thediameter of the electrode 1 and generally equal to the inner diameter ofthe tubular third electrode 3. This configuration provides a mimimumcontact area between member 6 and electrode 3 since only i the end edgeat end 3a of electrode 3 is in 'contact with a rim side wall at end 60of member 6.

As may be seen in the drawing the dished members 4 and 6 are generallycoaxially aligned with their first ends 4a, 6a closest to each other,their grooves 4c, 60, facing each other and their second ends 41;, 6b,spaced the grooves distance from each other. A tubular insulating ring21 is positioned with its opposite end edges received in the grooves 40and 6c. The tubular insulating ring 21 is of a ceremic material and hasits ends sealed in the grooves 40, 60 by means of a glasssealingmaterial to provide a gas tight seal between the edges of theinsulating rings 21 and the grooves 40, 60. Where theinsulating ring 21may be of a metallized ceremic it is contemplated by the inventionherein that it could be soldered into the grooves to form a gas tighthousing. With thisconstruction the first end cap means 11 is inelectrical contact with the first electrode 1 and in electrical contactwith the third electrode 3 by means of the second dished member 6contacting the first end of the third electrode 3a about its first end6a. The insulating ring 21 is of a length so that the first ends 4a, 6a

of the dished members 4 and 6 respectively are spaced from each other. I

The connection of the insulating ring 21 with thefirst and thirdelectrodes to form a gas tight excess voltage given off by theelectrodes during operation of the excess voltage arrester. In addition,the seams or joints of the discharge tube or arrester 10 which are themost critical to the vacuum tightness of the arrester, namely themetallic-insulating ring connections, are portected because the metallicparts 4 and 6 have thinner walls then the adjacent electrodes.Accordingly, the vacuum tight connection between the metal andinsulating material of the insulating ring 21 is not thermicallystressed. To prevent the metallic portions 4 and 6 which are connectedto the insulating ring 21 from being heated by passing currents, amassive contact member 8 is provided on the outer end lb of theelectrode l. The contact member 8 extends in anaxial direction beyondthe end of the end cap means 11 so that the currents which flow throughthe arrester are not guided via the metal parts of the discharge tubewhich are connected with the insulating rings, but are guided onlythrough the massive contact members 8. For a similarreason the contact18 of the. third electrode 3 also extends radially outwardly beyond thediameter of the discharge tube 10. The extension of the contact members8, 18 and 28 also has the advantage that the end cap means are protectedwhen the voltage arrester is handled or mounted.

The end cap means 12 may be constructed indentical to the constructionheretofore described with regard to the end cap 11 and the correspondingparts and elements have been indicated with a prefix 2 before thereferences numerals of the end cap 11.

The electrodes 1 and 2 and particularly their inner ends 1a and 2a areof a material such that when the arrester is overloaded the tips la and2a will melt off and contact the third electrode 3 to create acontinuous short circuit. Another advantage of the constructionaccording to the invention is that the coaxial arrangement of theelectrodes causes a lower reaction-impact voltage then washeretoforepossible with the prior art. Moreover, the reaction-impact voltage maybe further improved by the preionizing of the gas which fills theinterior of the discharge tube 10. For this purpose it is possibleaccording to the invention herein to add to the insulating rings 21 and22 a spot of material made of a radioactive substance or to add aradioactive gas-like substance such as tritium or crypton to the gasfilling. From the foregoing description of the invention it may be seenthat thedeficiencies of the prior art had been overcome by the veryefficient and'compact construction of my excess voltage arrester 10. Itis again emphasized that the frusto conical shape of the dished members4, 6, 24, 26, provides a certain elasticity to' the metallic parts whichconnect the electrodes with the insulator rings whereby the possibilityof fracture of has.

thedischargetube is greatly reduced. It will be undertended to belimitedonly by th'eappended claims. Al-

though minor modifications might be suggested by those versed in theart, it should be understood that I wish to embody within the scope ofthe patent warranted hereon all such modifications as might reasonablyand properly come within the scope of my contribution to the'art. I

I claim as my invention: 1. In a gas discharge excess voltage arrester,first and second axially aligned electrodes, each having an inner andouter end interconnected by a side surface, said electrodes extendingtoward one another so that said electrodes are spaced from each otheronly at-their adjacent inner ends; a third electrode having two endsurfaces interconnected by a side surface, said third electrode sidesurface being substantially uniformly spaced radially from said firstand second electrode side surfacesand surroundingand extending alongsaid first and second electrode side surfaces for a greater portion ofthe length thereof; dished endcap means for each end 'of said thirdelectrode, each end cap means having a frusto-conical' wall portionextending from an end of said third electrode inwardly therealong anddiverging therefrom, each end cap means having a first rim extendingradially inwardly of an outer end portion of said frusto-conical walland having an inner rim side wall in direct contact with an end surfaceof said third electrode, and each end cap means having a second rimextending radially outwardly of an inner end portion of saidfrusto-conical wall and an axially extending flange at the end of saidsecond rim and with said frusto-conical wall and said second rim forminga sealing groove; 7

dished end cap means for said outer ends of said first and secondelectrodes, each end cap means being spaced inwardly of said outer endsof said first and second electrodes, each end cap means having afrusto-conical wall portion extending towardv an outer end of anassociated electrode and diverging therefrom, each end cap means havinga first rim outer end portion of saidfrusto-conical wall and an axiallyextending flange at the end of said second rim and with saidfrusto-conical wall and said second rim forming a sealing groove;

inslulator rings in said sealing grooves spacing said first, second andthird electrodes in a spaced-apart relation with respect to each other;i

means sealing said v insulator" rings to said sealing grooves to form agas-discharge container having at least two discharge paths, wherein theinner surface of said insulator rings are screened off from saiddischarge paths by at least one of said frustoconical walls connectedbetween said electrodes and said insulator rings and wherein the wallthicknesses of said frusto-conical walls is less than the wall thicknessof said electrodes so as to minimize energy transfer between saidelectrodes andsaid walls; and

massive contact members on-each of said electrodes extending outwardlyof said electrodes and end cap means in both axial and radialdirections.

2. The excess voltage arrester of claim 1,

wherein the metallic end caps at each end of the arrester are opposed toone another, and Y wherein the insulating member is of such a length asto space said end cap means from each ohter and to hold the adjacentends of said first and second electrodes in spaced relation with respectto each other.

3. The excess voltage arrester of claim 2,

wherein said insulating rings is of a ceramic material and sealing meansare provided to seal said ring in said grooves at its ends to form a gastight connection.

4. The excess voltage arrester of claim 3,

wherein the first and second electrodes have cylindrical heads at theirouter ends of larger diameters than the diameters of said electrodes andabutted by said dished end cap means to proivide massive contacts andspace the adjacent ends of said first and second electrodes from eachother.

5. The excess voltage arrester of claim 4, wherein said gas dischargecontainer contains a gas preionized by a substance in said tube.

6. The excess voltage arrester of claim 5, wherein said third electrodehas an integrally formed radial flange portion extending outwardly ofsaid side surfaces thereof between said end cap means at the outer endsof said third electrode to form a massive contact membet on said thirdelectrode.

1. In a gas discharge excess voltage arrester, first and second axiallyaligned electrodes, each having an inner and outer end interconnected bya side surface, said electrodes extending toward one another so thatsaid electrodes are spaced from each other only at their adjacent innerends; a third electrode having two end surfaces interconnected by a sidesurface, said third electrode side surface being substantially uniformlyspaced radially from said first and second electrode side surfaces andsurrounding and extending along said first and second electrode sidesurfaces for a greater portion of the length thereof; dished end capmeans for each end of said third electrode, each end cap means having afrusto-conical wall portion extending from an end of said thirdelectrode inwardly therealong and diverging therefrom, each end capmeans having a first rim extending radially inwardly of an outer endportion of said frusto-conical wall and having an inner rim side wall indirect contact with an end surface of said third electrode, and each endcap means having a second rim extending radially outwardly of an innerend portion of said frusto-conical wall and an axially extending flangeat the end of said second rim and with said frusto-conical wall and saidsecond rim forming a sealing groove; dished end cap means for said outerends of said first and second electrodes, each end cap means beingspaced inwardly of said outer ends of said first and second electrodes,each end cap means having a frusto-conical wall portion extending towardan outer end of an associated electrode and diverging therefrom, eachend cap means having a first rim extending radially inwardly of innerend portions of said frusto-conical wall and having rim end walls indirect contact with the adjacent side surfaces of the associatedelectrode, and each end cap means having a second rim extending radiallyoutwardly of an outer end portion of said frusto-conical wall and anaxially extending flange at the end of said second rim and with saidfrusto-conical wall and said second rim forming a sealing groove;inslulator rings in said sealing grooves spacing said first, second andthird electrodes in a spaced-apart relation with respect to each other;means sealing said insulator rings to said sealing grooves to form agas-discharge container having at least two discharge paths, wherein theinner surface of said insulator rings are screened off from saiddischarge paths by at least one of said frusto-conical walls connectedbetween said electrodes and said insulator rings and wherein the wallthicknesses of said frusto-conical walls is less than the wall thicknessof said electrodes so as to minimize energy transfer between saidelectrodes and said walls; and massive contact members on each of saidelectrodes extending outwardly of said electrodes and end cap means inboth axial and radial directions.
 2. The excess voltage arrester ofclaim 1, wherein the metallic end caps at each end of the arrester areopposed to one another, and wherein the insulating member is of such alength as to space said end cap means from each ohter and to hold theadjacent ends of said first and second electrodes in spaced relationwith respect to each other.
 3. The excess voltage arrester of claim 2,wherein said insulating rings is of a ceramic material and sealing meansare provided to seal said ring in said grooves at its ends to form a gastight connection.
 4. The excess voltage arrester of claim 3, wherein thefirst and second electrodes have cylindrical heads at their outer endsof larger diameters than the diameters of said electrodes and abutted bysaid dished end cap means to proivide massive contacts and space theadjacent ends of said first and second electrodes from each other. 5.The excess voltage arrester of claim 4, wherein said gas dischargecontainer contains a gas preionized by a substance in said tube.
 6. Theexcess voltage arrester of claim 5, wherein said third electrode has anintegrally formed radial flange portion extending outwardly of said sidesurfaces thereof between said end cap means at the outer ends of saidthird electrode to form a massive contact member on said thirdelectrode.